The objectives of this study are: to compare the effects of cigarette smoking, low level carbon monoxide administered intermittently to produce similar levels, or CO as those produced by cigarette smoking and placebo (air inhalation) for 5 days each on cardiovascular hemodynamics including blood pressure, heart rate, catecholamine release and coagulation and; to compare effects of low level carbon monoxide on drug metabolism using nicotine and caffeine as probes of drug metabolism.